Loader I Buggered Up My Loader

[herringchoker]

KubotaB7800, LA402 loader, 830 hours. Fluid was seeping around the rod on both bucket cylinders and one boom cylinder, and the loader leaked down slowly. So I rebuilt those three cylinders using genuine Kubota rebuild kits, reassembled everything and topped up the hydraulic fluid. I have cycled the circuits to bleed air.
Now there is a problem. The bucket works fine but the boom is erratic:

• The boom is extremely slow to raise, except if I curl back or dump the bucket while at the same time raising the boom, the boom raises as normal only after the bucket is fully dumped or fully curled.
• If I try to start raising the boom with the bucket fully dumped or fully curled, the boom is still slow. (The full extension or retracting of the bucket cylinders while the boom is raising seems to be the only way to kick the boom into normal lift.)
• When I first pull back the lever to raise the boom (if the bucket is not on the ground), the boom actually drops first about 2” at the bucket.
• The boom will not lift the front of the tractor.
• If I try to lift the front of the tractor using the bucket, all it does is collapse the boom cylinders.
• There are no obvious external leaks or seeps.

The dipstick shows full fluid. I cracked the line to the pressure end of the rebuilt boom cylinder while the boom was raised and fluid seeped out.
I had detached the loader to make it easier to get at things. After reattaching the loader I re-checked the hydraulic quick connects...they look OK.

I'm confounded more than usual. Everything worked fine before I took things apart. Anyone have any ideas?

 

[ptsg]

Sounds like you either crossed some lines during reassembly or you have crossed the quick disconnects.

You may want to double check that.

 

[LouNY]

most likely crossed someplace.

 

[herringchoker]

most likely crossed someplace.

Thanks, guys. Makes sense so I went out and double checked lines and disconnects. They are all good, they're colour coded so easy to trace. I think I'll sleep on it and maybe take apart the rebuilt boom cylinder to see if I messed up inside that.

 

[greenie]

Interesting.... When you figure it out would you post what the solution was? We had a L3400 and in below freezing weather the bucket wouldn't operate but the boom would. Never did figure that out but I assumed it was in the spool assembly (lever control assembly).

 

[mrmikey]

May sound odd but any chance you could have put the boom seals in backwards?

 

[herringchoker]

May sound odd but any chance you could have put the boom seals in backwards?

I don't think so, but that's where I'm looking next (I have been wrong before!). The piston seals have to seal in both directions...the external seal against the barrel is two pieces, an inner square section rubber ring and a synthetic square section ring on top of it. That synthetic seal is a bugger to install, have to stretch it to get it in place and then carefully compress it into the groove on top of the rubber ring while not twisting it. The piston is sealed against the rod by a tiny rubber o-ring that has to be slid over the threaded end of the rod, so chance for damage there too.
The gland seals have to seal in one direction only so they can be installed backwards. There is no apparent external leak, so I think they are okay.
Anyway, I'm about to dive in and see what's there.
Will keep posting what I find.

 

[herringchoker]

Interesting.... When you figure it out would you post what the solution was? We had a L3400 and in below freezing weather the bucket wouldn't operate but the boom would. Never did figure that out but I assumed it was in the spool assembly (lever control assembly).

Will definitely do.

 

[dodge man]

Did you take the quick connects off and back on just to make sure they are seated. I’ve owned a tractor 14 years and twice I’ve not got them seated. They 100% look ok and won’t pull loose but aren’t on correctly. I’ve actually had things work backwards when this happens.

 

[CH4Ohio]

I don’t think your problem is inside a cylinder.

 

[herringchoker]

Problem found. I may have to fire the guy that installed this. As I suspected, that square section yellow synthetic ring must have been twisted and probably started to roll out of the groove between the two green split rings as I was installing the piston onto the rod. It then got caught up in the

yellow and black gland seals on the left. This was the first of the three rams I worked on. On the next two I used a hose clamp to squeeze the synthetic ring evenly into the groove on top of the rubber ring. That is even tricky because the synthetic ring has to be stretched out of shape to fit over the piston. I think something like an exhaust pipe expander would be great to stretch the yellow seal evenly so it would slide over the piston for installation. Anyway, I've been suspended for bad job performance and have the rest of the day off.

 

[CH4Ohio]

I rebuilt all 4 cylinders on my LA402 loader this winter. The factory color-coded dust covers were so faded they were useless. I wrapped duct tape around each hose and marked it with a Sharpie. Seemed like a good plan.

By the time I had gotten hydraulic fluid on things and wiped down and sprayed fasteners, etc., I realized that I’d washed my magic marker notes off. Duh!

I tried several times but couldn’t get them right. The loader did all kinds of crazy stuff. Finally had to use a shop manual and trace everything from end-to-end. I used colored wire ties to mark things. Won’t take it off again unless it’s clearly marked.

Sounds to me like you have switched lines on cylinder(s) or it’s switched at the QD.

PS. After the first cylinder, I decided not to change that middle wiper gasket. It’s ridiculous how hard it is to get it stretched out and then it’s sloppy. That one looked good on every cylinder and doesn’t cause external leakage anyway. Made the remaining 3 cylinders super easy to rebuild.

 

[CH4Ohio]

As Emily Litella used to say, “Nevermind ….”

 

[CH4Ohio]

Problem found. I may have to fire the guy that installed this. As I suspected, that square section yellow synthetic ring must have been twisted and probably started to roll out of the groove between the two green split rings as I was installing the piston onto the rod. It then got caught up in the View attachment 3685241yellow and black gland seals on the left. This was the first of the three rams I worked on. On the next two I used a hose clamp to squeeze the synthetic ring evenly into the groove on top of the rubber ring. That is even tricky because the synthetic ring has to be stretched out of shape to fit over the piston. I think something like an exhaust pipe expander would be great to stretch the yellow seal evenly so it would slide over the piston for installation. Anyway, I've been suspended for bad job performance and have the rest of the day off.

Not your fault. Those things are terrible to install. I ended up heating one in near boiling water and still fought it. Of course it was sloppy loose when I finally did get it over the middle groove.

 

[dodge man]

Glad you found the problem!